1. Field of Invention
The present invention relates to a method for determining the number and size of resin particles freely distributed in paper stock.
2. Description of the Prior Art
In papermaking by a procedure at neutral pH, the natural resin particles present in the paper stock give rise to problems. In particular, the free resin particles, ie. those which are not bound to the wood fibers, are deposited in the paper machines and hence lead to considerable operating problems, for example tears in the paper, and consequently to expensive downtimes. Assistants which bind the resin particles to the wood fibers and thus ensure that the resin is discharged with the paper from the paper machine are therefore added to the paper stock. The efficiency of such assistants has been tested to date by expensive and not very reliable tests on the paper machines themselves. Furthermore, the literature describes methods which permit determination of the harmful amount of resin in the laboratory. However, the detection of free resin particles and testing of the efficiency of the assistants used is made very difficult on the laboratory scale by virtue of the fact that the unbound resin is present only in very small amounts in the paper stock (about 1 g of free resin to 1 tonne of paper stock). The known, conventional methods of determination of harmful resin, such as the extraction of the paper stock with organic solvents, for example with dichloromethane (Weigl et al., Das Papier 40 (1986), V52), the deposition of the resin on surfaces, for example according to Gustafson (Gustafson C. et al., Paperi ja Puu 34 (1952), 121-127), the flotation method according to Storle and Teves (Storle and Teves, Das Papier 10 (1956), 264-170) and the microscopic counting method (Allen, L. H., Pulp & Paper, Canada, 76 (1975), 70) thus give unsatisfactory and controversial results.